Energy Fuels 2009, 23, 4974–4980 Published on Web 09/10/2009
: DOI:10.1021/ef900370v
Effects of a Platinum-Cerium Bimetallic Fuel Additive on the Chemical Composition of Diesel Engine Exhaust Particles Tomoaki Okuda,*,†,‡ James J. Schauer,† Michael R. Olson,† Martin M. Shafer,† Andrew P. Rutter,† Kenneth A. Walz,§ and Paul A. Morschauser§ † Environmental Chemistry and Technology Program, University of Wisconsin;Madison, 660 North Park Street, Madison, Wisconsin 53706-1413, ‡Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan, and §Madison Area Technical College, 3550 Anderson Street, Madison, Wisconsin 53704-2599
Received April 25, 2009. Revised Manuscript Received August 29, 2009
The use of a platinum-cerium bimetallic fuel additive has been proposed as a cost-effective strategy for reducing particulate matter (PM) and NOx emissions from diesel-powered engines. Although previous studies have demonstrated that the use of platinum-cerium bimetallic fuel additive reduced emissions from diesel engines, there have been no reported investigations of how the use of these fuel-borne catalysts (FBCs) impact the chemical and physical properties of diesel PM emissions. The present study demonstrates that the use of a platinum-cerium bimetallic fuel additive has a significant impact on the detailed chemical composition and size distribution of PM emitted from a diesel engine. Tests were conducted to explore the impact of different fuel concentrations of the fuel-borne catalyst at different engine-operating conditions. These tests were performed with a medium-duty diesel engine that was not equipped with exhaust gas recirculation or a diesel particulate filter (DPF). The results demonstrated that the use of the additive significantly reduced the emissions of PM2.5 and carbonaceous species. The reduction was 34% for the PM2.5 mass, 54% for the PM2.5 elemental carbon, and 23% for the PM2.5 organic carbon when 0.1 ppm Pt and 7.5 ppm Ce of the additive were used. Emissions of particle-phase metals originating from the additive had a significant contribution to particle matter emissions when 0.7 ppm Pt and 42 ppm Ce of the additive were used. The particle size distribution of platinum in the PM emissions was different from the size distribution of cerium. The cerium/ platinum ratio in the PM2.5 diesel particle emissions ranged from 119 to 656, which was much higher than the ratio in the fuel additive that was 58.5 ( 5.6, indicating a higher penetration of cerium through the engine.
more efficiently if engine development is coupled with diesel fuel reformulation and/or the use of fuel additives.6,7 Metalbased additives have been reported to be effective in reducing diesel emissions in two ways: (1) the metals react with water vapor in the exhaust emissions to produce highly reactive hydroxyl radicals, and (2) the metals serve as an oxidation catalyst and thereby lower the oxidation temperature for diesel soot and lead to increased particle burn out.8-10 Usually, the fuel-borne catalyst (FBC) is added as an organometallic compound and emitted in the exhaust as a particulate phase oxide, often present as nanometer-sized particles formed by the homogeneous nucleation of the oxidized additive.11,12 A variety of FBCs were studied in the past, including cerium (Ce), iron (Fe), cerium-iron (Ce-Fe), platinum (Pt), platinumcerium (Pt-Ce), manganese (Mn), and copper (Cu).12-14 The
1. Introduction Diesel engine exhaust emissions contribute significantly to urban and global air pollution.1,2 Regulatory agencies worldwide have been tightening emissions standards for diesel engines as the weight of evidence documenting the toxicity of diesel particulate matter (PM) accumulates.3-5 Although the improvements in the modern diesel engine design and combustion conditions have led to significant reductions in both NOx and PM emissions, these reductions have not been sufficient to meet new standards without additional control measures. Further reductions in emissions can be achieved *To whom correspondence should be addressed. Telephone/Fax: þ81-(0)45-566-1578. E-mail:
[email protected]. (1) Finlayson-Pitts, B. J.; Pitts, J. N. Chemistry of the Upper and Lower Atmosphere: Theory, Experiments, and Applications; Academic Press: San Diego, CA, 2000. (2) United States Environmental Protection Agency (U.S. EPA). National Air Pollutant Emission Trends Update 1970-1997, EPA 454/E-98007. U.S. Government Printing Office, Washington, D.C., 1998 (3) European Commission. Directive 2005/55/EC of the European Parliament and of the Council and Directive 2005/78/EC, OJ L 192, 19.7.2008, 2008; pp 51-59. (4) Ministry of Land, Infrastructure, and Transport, Japan. Official Gazette, March 25, 2008, 348. (5) United States Environmental Protection Agency (U.S. EPA). EPA’s Program for Cleaner Vehicles and Cleaner Gasoline, EPA420F-99-051, 1999. (6) Ulrich, A.; Wichser, A. Anal. Bioanal. Chem. 2003, 377, 71–81. (7) He, B.-Q.; Shuai, S.-J.; Wang, J.-X.; He, H. Atmos. Environ. 2003, 37, 4965–4971. r 2009 American Chemical Society
(8) Yang, H. H.; Lee, W. J.; Mi, H. H.; Wong, C. H.; Chen, C. B. Environ. Int. 1998, 24, 389–403. (9) Kasper, M.; Sattler, K.; Siegmann, K.; Matter, U.; Siegmann, H. C. J. Aerosol Sci. 1999, 30, 217–225. (10) Miyamoto, N.; Hou, Z.; Harada, A.; Ogawa, H.; Murayama, T. SAE Trans. 1987, 96 (871612), 792–798. (11) Burtscher, H.; Matter, U.; Skillas, G. J. Aerosol Sci. 1999, 30, S851–S852. (12) Jelles, S. J.; Krul, R. R.; Makkee, M.; Moulijn, J. A. Catal. Today 1999, 53, 623–630. (13) Campenon, T.; Wouters, P.; Blanchard, G.; Macaudiere, P.; Seguelong, T. SAE Tech. Pap. 2004-01-0071, 2004. (14) Jelles, S. J.; Makkee, M.; Moulijn, J. A. Top. Catal. 2001, 16/17, 269–273.
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Energy Fuels 2009, 23, 4974–4980
: DOI:10.1021/ef900370v
Okuda et al.
use of organo-platinum FBCs with and without efficient postcombustion filtration has been demonstrated to significantly reduce tailpipe emissions of regulated air pollutants and smog precursors,15 whereas fuel-borne Pt catalysts are currently approved in the U.S. for use in many specialty diesel vehicles and applications are pending for broader use. The use of a platinum-cerium bimetallic fuel additive represents a potential promising strategy for controlling emissions from diesel engines because the temperature of which the Pt-Ce additives (in this case, 0.5 ppm Pt and 5 ppm Ce) efficiently catalyzed the oxidation of soot was the lowest (in this case, 275-300 °C) among the many combinations of fuel additives.12,14 The inorganic and organic composition of fine PM emitted from diesel-powered motor vehicles, with and without aftertreatment devises, has been the subject of several studies,16-19 which has been used in numerous source apportionment studies, air-quality models, climate-change models, and health-effect studies;20-24 however, very few studies have addressed the chemical characteristics of diesel PM when FBCs were used.8,25,26 Even less information is available on the emission characteristics of diesel engine exhaust particles where a platinum-cerium bimetallic fuel additive was applied. The characterization of diesel engine emissions using a novel fuel amendment technology allows us to proactively understand future air pollution problems and prevent potential problems before the widespread adoption of the technology increases the inertia of the market to a level where even small changes are difficult. This paper demonstrates the significant impact of the use of a platinum-cerium bimetallic fuel additive on the detailed chemical composition of PM emitted from a diesel engine.
Table 1. Experimental Matrix for Bimetallic Fuel Additive and Engine Operations test code additive concentration (ppm Pt) additive concentration (ppm Ce) start modea engine speed (rpm) torque (N m) engine power (bkW)
D1
D2
D3
D4
D5
D6
D7
D8
0.13 0.13 0.13 0.13 0.70 0.70
cold 1600 225 36
hot 1600 224 36
7.5
7.5
7.5
7.5
42
42
cold 1600 225 36
hot 1600 224 36
hot 700 38 2
hot 1600 674 107
hot 1600 226 37
hot 1600 226 36
a A cold-start sampling was started at the time when the engine was started. A hot-start sampling was started 2 h after the engine had been running.
Table 2. Properties of Fuel Used in This Study analysis
value
density at 15 °C (g/cm3) gross heating value (BTU/lb.) carbon (wt %) hydrogen (wt %) nitrogen (wt %) oxygen (wt %) sulfur (wt %) ash (wt %)
0.870 ( 0.001 19400 ( 283 86.94 ( 0.04 12.53 ( 0.08
